Title

Inert Gas Measurements in the Apollo 16 Drill Core and Evaluation of the Stratigraphy of this Core

Document Type

Conference Proceeding

Publication Date

1978

Department

Physics and Astronomy

Abstract

Inert gas measurements on a large number of < 1 mm fines from barrels 60003 and 60002 of the Apollo 16 drill core are discussed in the context of a survey of the entire core. We show or confirm that the mixing of three major soil components, called α, β, γ, is a major Leitmotiv of the core, and that these soil components have close relatives among the soils now at the surface of the regolith at Apollo 16 and in the double drive tube 60009/60010. Most soils in the core are therefore locally (within 5-10 km) derived. We discuss three categories of boundaries between dissection units (DU's): 1 major, well-established stratigraphic breaks which are buried surfaces (DU 12/DU 13 and DU 43/ DU 44); 2 stratigraphic breaks which may also be time-stratigraphic boundaries (DU 9/ DU 10; DU 5/DU 6; DU 27 /DU 28); and 3 stratigraphic breaks for which supporting evidence is weak, and which need more study (DU 17/DU 18; DU 24/ DU 25; DU 13/DU 14; DU 31/DU 32; DU 45/DU 46; DU 34/DU 35; and DU 3/ DU 4). We suggest the following depositional history: 1 MPV-A (Modal Petrologic Unit) represents deposition, probably inside a secondary crater, in a boulder-strewn environment (the boulders were predominantly light matrix breccia); 2 when the boulders were essentially comminuted, a sub-unit called MPU-B03 was deposited by further filling in of the crater from its own walls; 3 the sub-unit called MPU-B04 may then have been emplaced as a single soil slab ranging from 13 to more than 45 cm thickness; 4 MPV-C represents again deposition in a boulder-rich environment (the boulders were plagioclase-rich): 5 MPU-D represents principally 3-rich soils "pushed" onto the core site by the North Ray Crater event or by the South Ray Crater event, or by both (MPU-D may therefore represent two discrete events; the break seems to occur at DU 45/ DU 46). Erosion may have occurred but cannot be firmly documented.

Publication Title

Proceedings of the Ninth Lunar and Planetary Science Conference

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